What would you have the maximum salary be (or total compensation, whichever metric you want), above which people are no longer entitled to unionize?
I don't do a very good job of clearly explaining the why aspect of my comment, however I did write an unreasonably long response to multiple comments further down that probably clarifies nothing but at least expands on my original comment. You can see it here: https://news.ycombinator.com/item?id=30449521